Modern communication devices, such as radio frequency (RF) communication devices, process electromagnetic wave signals with variable signal strength. The variable signal strength varies depending on distance between a transmitter and a receiver, as well as environmental factors and process, temperature etc. variations (PVT). A power amplifier (PA) is utilized prior to signal transmission by a transmitter, for example, and a variable gain low noise amplifier (LNA) is utilized after a signal is received by a receiver, to amplify the signal and adjust the signal gain accordingly. Conventional gain control circuits in a signal amplifying device, however, do not improve the linearity of the PA and/or LNA that is utilized for signal amplification.
Different gain control techniques are utilized by conventional gain control circuits in signal amplifying devices without accounting for PVT. For example, amplifier gain in a conventional LNA or PA devices is varied by changing the resistance of one or more resonance tanks in the conventional LNA or PA. A resonance tank may comprise one or more LC circuits, for example, adapted to resonate at a determined frequency. By changing the inductance (L) and/or capacitance (C) of the LC tank, the overall tank resistance may be changed and, as a result, the LNA's or PA's gain may be changed as well. This technique, however, does not compensate for gain variations in the core amplifier circuit due to PVT.
Other conventional gain control techniques utilize PMOS transistor switches to implement low gain and high gain amplification within an exemplary LNA or PA. For example, if the PMOS transistor is turned off, high gain control may be applied by the exemplary LNA or PA. Similarly, if the PMOS transistor is turned on, low gain control may be applied by the LNA or PA. PMOS transistors utilized in conventional variable gain LNA and PA devices, however, cause high parasitic capacitance and increase overall device non-linearity since variations, such as PVT, in the core amplifying circuit are not tracked during an operation cycle. As a result, non-linearity decreases amplifier sensitivity and contributes to the creation of intermodulation (IM) products in the desired signal passband.
Amplifier circuits utilizing a conventional variable gain LNA comprise one or more downconversion mixers followed by a bandpass filter. After a signal is amplified by the variable gain LNA, it may be downconverted by the downconversion mixer, preserving the wideband signal characteristics of the amplified signal. The signal may then be bandpass filtered resulting in a narrow band signal. To improve the LNA sensitivity and increase amplifier linearity, conventional circuits utilize received signal strength indicators (RSSI) after an incoming signal is communicated from the LNA. The received signal strength indicators may provide gain control feedback signals to the LNA for gain adjustment. Such received signal strength indicators, however, require circuits that utilize significant on-chip real estate. In addition, in order to obtain good gain control feedback signal, an amplifier circuit requires numerous received signal strength indicators.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.